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Written By: Andrea
plastic board (1)
crooked plastic lever (1)
An earthquake detector can be a useful home safety device because it alerts you to a quake
some seconds before it happens. During an earthquake two kinds of waves are emitted from
the centre: a small wave and a dangerous wave. The small wave is faster, so it is the first
sign of the event if your house is located some kilometres away from the centre.
An earthquake detector could also work in combination with other devices, such as a gas
This device consists of a highly sensitive lever which is hooked to a spring. A weight is fixed
at the end of the lever by an M8 screw. The lever should resonate with a frequency of about
2 HZ. When the sensor shakes, an M3 screw fixed on the lever will touch the horizontal
spring, and it will close a delay-off circuit which drives a piezoelectric buzzer.
Construction drawing (pdf)
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Step 1 — Earthquake Detector
• Make the holes on the plastic
board: 3 millimetres in diameter for
the springs' anchor bolts (affix
three M3 screws); 4 millimetres in
diameter for the lever fulcrum (affix
an M4 screw).
• Make the bearing housing on both
sides of the lever: drill 8
millimetres in diameter on full
depth; 9 millimetres in diameter on
• Make the hole for the spring anchor
bolt (M3 screw) on the lever.
• Make the hole for the switch screw
on the lever.
• Affix an M8 screw with a weight (I
used some screw nuts) at the end
of the lever.
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• Affix the springs and the lever on
the board using self-lock screw
• Put washers on both bearings (I
used brass washers).
■ Do not overtighten the M4
screw nut on the bearings;
otherwise the lever will not be
• Connect a wire to the static anchor
bolt of the lever spring.
• Connect the moving anchor bolt of
the lever spring to the switch screw
(you'll see a red wire jumper).
• Connect a wire to the horizontal
• Connect the free ends of the wires
to a delay-off bell circuit.
It works quite fine, though some details need to be fixed.
This document was last generated on 201 2-1 1 -03 03:48:59 AM.
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